1. Field of the Invention
The present invention relates to improvements in polymeric bags. Specifically, the present invention relates to polymeric bags utilizing a drawstring and typically used for trash or refuse disposal. Moreover, the present invention relates to polymeric bags utilizing a drawstring which is intended to be elastic or elastic-like in performance.
2. Description of the Related Art
Polymeric bags are ubiquitous in modern society. Polymeric bags can be manufactured using woven polymeric materials or manufactured using thin polymeric films with one or more material layers. Applications for which polymeric bags may be utilized are numerous with variations of polymeric bags used in a number of different industries. Moreover, some polymeric bags may exhibit certain properties depending on the specific polymeric materials used in the manufacturing process.
The present invention relates primarily to thin-film bags, typically polyethylene bags, used for trash or garbage collection. Such bags are typically manufactured using a blown-film extrusion process, providing a film material for the trash bag body which is subsequently converted into a final product. Polyethylene trash bags are available in different sizes, thicknesses, and colors and typically incorporate one of three different closure methods: straight top bags with twist tie closures; flapped bags where the flaps can be used to secure, tie, and carry the bag; and drawstring trash bags where a drawstring is provided within each hem to provide a method for securing, tying, and carrying the trash bags. The present invention is of particular relevance to drawtapes used in drawstring trash bags.
Over the past decade drawstring trash bags have enjoyed increasing commercial success as consumers recognize such bags increased utility. This is particularly true with respect to domestic, household use where drawstring trash bags are now the most popular type of trash bags used in kitchen settings.
Such drawstring bags typically feature a drawstring located within each hem and anchored to the upper corners of the bag. The drawstrings can be used to pull the trash bag closed, to secure the trash bag mouth closed by tying the drawstrings closed, and to provide handles for carrying the closed, filled trash bag. Traditionally, such drawstrings were manufactured using primarily high density polyethylene, which offers increased tensile strength when compared to linear low density polyethylene or low density polyethylene. However, new improved drawstrings are emerging which provide other features and functions, particularly with respect to securing the top of the drawstring trash bag onto a trash receptacle.
One solution for gripping the top of a trash receptacle is described in U.S. Pat. No. 5,133,607 entitled “Plastic Liner Bag with Elastic Top Tie Strip.” The '607 patent, which is incorporated herein by reference, describes using an elastic drawstring or band within the top of the drawstring bag. The elastic drawstring can be pulled outward at the top corners of the bag. Unfortunately, the elastic tie top disclosed requires relatively expensive elastomeric materials and a thicker gauge than traditional high density drawstrings.
A different approach to drawstrings in trash bags is disclosed in United States Published Patent Application Nos. 2003/0072505 and 2004/0097357, both of which are entitled “Techniques for Making Mono-Axially Oriented Draw Tape Which is Usable in a Draw Tape Bag.” These references disclose a technique for making mono-axially oriented drawtape by forming a solid sheet of thermoplastic material and subsequently stretching and annealing the film to create a set of drawtape rolls. The stretching and annealing process orients the molecules within the drawtapes to ostensibly provide increased tensile strength along the length of the drawtape. More specifically, it is claimed that the oriented drawtape can provide increased strength over non-oriented drawstrings of the same gauge.
United States Published Patent Application No. 2005/0063622, entitled “Blended Polymeric Draw Tapes,” describes oriented single-layer film. In this reference and the two previously described oriented tape references, the process described is known as machine-direction orientation (MDO). A person of ordinary skill in the art would understand that the MDO process involves a procedure for orienting film by heating the film to a point at or near the melting point and then stretching the material to a length several times the original length. After the stretching process is complete, the film is cooled either naturally or by using cooling rollers to anneal the film, locking the film into the oriented state. One example described in the '622 application discusses taking 9 mil thick blown-film tape and orienting it in the machine direction so that a 1.3 mil tape results.
For the MDO processes described in the foregoing references, the film is heated to a temperature above the Vicat softening point. The Vicat softening point is the point where polymeric materials, including those described in the foregoing references, begin to soften and transition into a molten state. The nature of polymeric materials means that each polymeric material is a distribution of different polymer molecules, or polymer chains. Each polymer molecule exhibits different properties based upon the length of the molecule, the branching structure, and other properties of the molecule. Thus, polymeric materials do not have a concrete, well-defined melting point as certain polymer molecules will transition to a molten state at different temperatures than other polymer molecules.
Below the Vicat softening point, a polymeric film exhibits the properties of a solid where the polymer molecules do not freely flow within the film. However, as the temperature of a film is increased above the Vicat softening point, a certain portion of the polymeric molecules begin to transition to a molten state. Even at this elevated temperature, a sufficient portion of the film remains solid enabling the film to be manipulated and stretched. However, if the temperature were increased even further, the film would soften to a point where the film, as a whole, becomes molten. Such a molten film would lack sufficient structure for the film to be manipulated in any way, such as in an MDO process. Thus, within the range of temperatures above the Vicat softening point, the softened polymeric film permits such film to be stretched, typically many multiples of the original length, in an MDO process. Absent such elevated temperatures, the same polymeric film would be permanently deformed, or yield, under the exact same tensile forces applied during the MDO process.
Another approach to improving drawstrings in trash bags is described in United States Published Patent Application No. 2011/0052103 entitled “Elastic Drawstring for Trash Bags.” The '103 application discloses a blend of linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) to provide a drawstring with elastic-like properties. Specifically, when the two polyethylenes are used together as described in the patent application, the resultant material provides some limited elastic-like properties, with the blended drawtape exhibiting a greater percentage of elongation before yielding than either of the two materials would exhibit by themselves. Moreover, a 3 mil drawtape according to the '103 application can provide elastic recovery of approximately 78%, which is greater than either the LLDPE or the LDPE would exhibit individually. However, it would be advantageous to further improve the properties of the tape described in the '103 application. The present invention describes such improvements.